Bob Costas warms up in the NBC studios at the Sochi Olympics. He'll return to hosting NBC Olympics Primetime on Monday, Feb. 17.

The longtime NBC primetime host was back at NBC's Olympic studios at the International Broadcast Center in Sochi on Sunday prepping for his assignment after missing six days of broadcasts with what he described as a viral eye infection. He will resume his primetime and late night hosting duties on Monday night. Matt Lauer, who filled in for Costas, last week, will host both programs Sunday.

Costas's absence on NBC's Olympic coverage broke a streak of 157 consecutive primetime appearances for the anchor on NBC's Olympic coverage between the Summer and Winter Games. Costas alerted viewers to his eye condition early in the Sochi coverage and eschewed contact lens for glasses while on the air. He had the infection treated by doctors NBC brought with them to Russia, but was unable to appear on air.

"It was becoming increasingly noticeable and uncomfortable, but if it was just that, I would have continued," Costas said last week. "We in broadcasting are lucky to have the jobs we do, and at one time or another, we've all gone on the air feeling less than our best. The difference is that last night and into this morning, it got to the point where, as a practical matter, I simply couldn't do my job because my eyes had become so blurry, watery and sensitive to light.

"If it was just discomfort, I'd be there. I'm receiving excellent treatment ... it's a viral infection, and all you can do is try to manage the symptoms while the virus runs its course."

NBC used Lauer and Meredith Vieira as replacements in Costas's absence. Why morning show veterans as opposed to a sports department staffer such as Rebecca Lowe, Al Michaels or Dan Patrick?

"As I’ve said we’ve got no shortage of candidates," said NBC Olympics executive producer Jim Bell, a former top executive of NBC's Today show, speaking to a handful of reporters on Friday. "Many of them are already working for us on the air, and I think that was really one of the considerations ... Meredith's schedule was a little bit looser so that’s why, and obviously, we have a relationship and have worked together ... So that made it a relatively easy decision and allowed us to keep the other parts of the operation running smoothly without needing to disrupt any other of the other day parts that we have or any shows that anyone else is doing.”

NBC Sports chairman Mark Lazarus said he had been checking in with Costas every day in Sochi.

"Bob did the first couple of days playing hurt and then regressed to the point where it was difficult for him to see and read and take light," Lazarus told SI.com on Sunday. "He became not an option. I've been hopeful every morning that he would be coming back that day. As nice as the hotel is here for us, it's not a place you want to sit around for five days."

An NBC spokesperson said Costas will wear glasses on the air tomorrow night. On Sunday he was testing his eyes and seeing how the lights affected them. Costas was at the International Broadcast Center on Sunday for about two hours, including time spent in meetings.